The hydroformylation of 3-pentenenitrile (3PN) to 5-formylvaleronitrile (5FVN) is an attractive route to produce nylon intermediates. As disclosed in U.S. Pat. No. 5,986,126, the reductive amination of 5FVN produces 6-aminocapronitrile and/or hexamethylenediamine, which are two key intermediates for the production of Nylon-6 and Nylon-6,6 respectively. The oxidation of 5FVN to 5-cyanovaleric acid, followed by hydrogenation to 6-aminocaproic acid, produces caprolactam, which is the monomer of choice to make Nylon-6.
A key element in the overall scheme is a stable catalyst that produces 5FVN by hydroformylation of 3PN. Typical catalysts involved in these reactions comprise a metal, such as rhodium, and an organic ligand, such as a bidentate phosphite. Such catalysts tend to deactivate upon recycle due to irreversible reactions believed to involve the metal center or the ligands coordinated to the metal center. In the case of hydroformylation of 3PN to 5FVN, the most active and selective catalysts comprise bidentate phosphite ligands.
When the hydroformylation of 3PN to 5FVN is performed in a continuous fashion, involving catalyst recycle, the catalyst loses activity continuously.
There is a need in the art, therefore, for making 5FVN in which the inactive form of the catalyst is reactivated.
This need is met by the present invention, which is a process for making 5FVN, comprising contacting in a reactor 3PN with CO and hydrogen in the presence of a catalyst comprising rhodium and a bidentate phosphite ligand to produce a product stream comprising 5FVN, unreacted 3PN and catalyst, separating at least a portion of said product stream into a low boiler fraction comprising 3PN and a major portion of the 5FVN and a high boiler fraction comprising a minor portion of the 5FVN and catalyst, contacting at least a portion of said high boiler fraction with hydrogen at a temperature in the range 50 degrees C. to 170 degrees C. and a pressure in the range 50 psig to 2000 psig to produce a hydrogen-treated high boiler fraction, and introducing at least a portion of said hydrogen-treated high boiler fraction into the reactor.